1. Field of the Invention
This invention relates to a process for producing a fluorine-containing acrylic or methacrylic polymer.
2. Description of the Related Art
In order to impart good surface properties such as releasability, stainproofing, water repellency and oil repellency to the surfaces of various adherends, it is common to apply coating agents containing a fluorine-containing acrylic or methacrylic polymer.
Such a fluorine-containing acrylic or methacrylic polymer is known to include polymers obtained by polymerizing fluorine monomers such as acrylic or methacrylic acid esters (both herein inclusively xe2x80x9cacrylate or methacrylatexe2x80x9d) having a polyfluoroalkyl group or perfluoroalkyl group having 6 to 16 carbon atoms. In this instance, the fluorine monomers are mostly copolymerized with non-fluorine monomers, and their copolymerization is widely carried out by solution polymerization or emulsion polymerization making use of general-purpose solvents.
Such copolymerization of fluorine monomers with non-fluorine monomers can make resultant copolymers highly soluble in the general-purpose solvents and also can achieved a low material cost, but on the other hand tends to make greatly poor the properties such as releasability and stainproofing that are inherent in fluorine-containing polymers.
Accordingly, when importance is attached to the properties inherent in the fluorine-containing polymers, the fluorine monomer must be used in a large proportion in the total monomer. Usually, the fluorine monomer must be in a proportion of at least 70% by weight in the total monomer.
Now, when polymerization is carried out under such conditions that the proportion of fluorine monomer in the total monomer exceeds 70% by weight, it is not preferable to employ emulsion polymerization which makes use of a surface-active agent in a large quantity. This is because the surface-active agent used may bleed to coating film surfaces to cause a deterioration of surface properties of coating films formed of fluorine-containing polymers.
One may contemplate employing bulk polymerization as one of polymerization methods, which, however, has a problem on the controllability of polymerization reaction, and also has a problem that the polymer is obtained as a hard mass that is difficult to handle, and is apt to turn into a gel when dissolved in a fluorine type solvent. Thus, it is not practical to employ the bulk polymerization.
Accordingly, it follows that solution polymerization is employed when polymerization is carried out under the conditions that the proportion of fluorine monomer in the total monomer exceeds 70% by weight.
In the solution polymerization, it is necessary to use a solvent capable of dissolving the fluorine monomer and also dissolving the fluorine-containing polymer formed. Such a solvent can not be any commonly available general-purpose solvents not capable of dissolving the fluorine-containing polymer, and fluorine type (PFC) or chlorine-fluorine type (CFC) solvents such as trichlorotrifluoroethane, metaxylene hexafluoride, tetrachlorohexafluorobutane and FC-726 (available from 3M) are used (see Japanese Patent Application Laid-open No. 61-23656 and Japanese Patent Publication No. 1-42983).
Since, however, the fluorine type or chlorine-fluorine type solvents are very expensive solvents compared with commonly available general-purpose solvents, there is a problem that they hinder the reduction of production cost for fluorine-containing polymers. To solve this problem, one may contemplate using the fluorine type solvent in a relatively small quantity (e.g., in an amount not more than 200 parts by weight) based on 100 parts by weight of the total monomer. This, however, may cause an increase in solution viscosity with progress of polymerization to not only make agitation very difficult but also make it very difficult to take out the resultant polymer from the reaction vessel.
The fluorine type or chlorine-fluorine type solvents have another problem that they are considered to destroy the ozone shield present in the sky on the earth and cause a rise of the earth s surface temperature. Thus, it is strongly required not to use them for the purpose of the conservation of terrestrial environment.
The present invention intends to solve the above problems the prior art has had. Accordingly, an object of the present invention is to make it possible to produce a fluorine-containing polymer having the fluorine monomer in a high proportion, by the use of commonly available general-purpose solvents without use of fluorine type solvents and chlorine-fluorine type solvents.
The present inventors have discovered that, when a non-halogen type solvent is used, a polymer-containing liquid phase comprised of (i) a fluorine-containing acrylic or methacrylic polymer formed with progress of polymerization and (ii) an organic solvent, with which the polymer is saturated, can be separated from the solution phase by controlling the type and amount of the solvent used, and when so polymerized as to cause such phase separation the reaction mixture containing the fluorine-containing polymer can be well stirred even when polymerized without use of any fluorine type solvent or chlorine-fluorine type solvent, so that the fluorine-containing polymer can be produced in a good efficiency. Thus, they have accomplished the present invention.
More specifically, the present invention provides a process for producing a fluorine-containing acrylic or methacrylic polymer, which comprises polymerizing a fluorine-containing acrylate or methacrylate in a solution phase formed of an organic solvent and dissolved therein a monomer containing a fluorine-containing acrylate or methacrylate having a polyfluoroalkyl group, wherein;
a non-halogen type solvent is used as the organic solvent and the fluorine-containing acrylate or methacrylate is so polymerized that a polymer-containing liquid phase comprised of the fluorine-containing acrylic or methacrylic polymer formed with progress of polymerization and the organic solvent is separated from the solution phase.
This and other objects, features and advantages of the present invention are described in or will become apparent from the following detailed description of the invention.
The present invention will be described below in detail.
The process for producing a fluorine-containing acrylic or methacrylic polymer according to the present invention is a process comprising polymerizing a fluorine-containing acrylate or methacrylate in a solution phase formed of an organic solvent and dissolved therein a monomer containing a fluorine-containing acrylate or methacrylate having a polyfluoroalkyl group.
In this process, a non-halogen type solvent is used as the organic solvent. Hence, the problem on production cost and the problem on terrestrial environment do not occur which may occur when the fluorine type or chlorine-fluorine type solvents are used.
In the production process of the present invention, the fluorine-containing acrylate or methacrylate is so polymerized that a polymer-containing liquid phase comprised of the fluorine-containing acrylic or methacrylic polymer formed with progress of polymerization and the organic solvent is separated from the solution phase which is uniform at the initial stage of the polymerization. Hence, the polymerization reaction can be made to progress in a good efficiency while keeping the polymer from turning into a gel during the reaction. The reason therefor is unclear, and is presumed as follows:
Because of the controlling of the type and amount of the non-halogen type solvent, the reaction mixture that forms a uniform solution phase at the initial stage of the polymerization is separated into two phases, a lower-layer phase and an upper-layer phase. The lower-layer phase is a polymer-containing liquid phase in which the resultant fluorine-containing acrylic or methacrylic polymer is contained in a large quantity and the organic solvent and fluorine monomer stand molten into the polymer in the quantities corresponding to their respective solubility. The upper-layer phase is a solution phase in which the fluorine monomer and an oligomer are dissolved in the organic solvent. Then, the polymerization separately proceeds in each phase, during which the respective components are kept in equilibrium by their diffusing movement, as so presumed.
Having been passed through such a polymerization process, the polymer-containing liquid phase that is rich in the fluorine-containing polymer is kept in a low viscosity during the polymerization reaction irrespective of a very high polymer concentration. Hence, the polymer-containing liquid phase can be stirred with ease until the polymerization is completed, and also the polymer thus formed can be simply taken out from the reaction vessel.
Having been passed through such a polymerization process, the polymer can also be obtained at a rate of polymerization that is high within a controllable range, and also can have a high degree of polymerization, but not so high a degree of polymerization as to turn into a gel. This is presumably because the polymer concentration in the polymer-containing liquid phase is sufficiently high enough to realize a high degree of polymerization, whereas, with regard to the rate of polymerization, the monomers consumed must be fed from the solution phase and hence the rate of their diffusion determines the rate of polymerization, so that the polymerization reaction does not run away. In this sense, the solution phase is presumed to function as a storehouse of monomers after the phase separation.
In addition, having been passed through such a polymerization process, the solution phase at the end of polymerization is comprised of an excess solvent having not completely being dissolved into the polymer formed, the fluorine monomer and the oligomer. Hence, the solution phase can be simply separated from the polymer-containing liquid phase. Also, when the quantity of the organic solvent is set a little smaller, most of the solvent is absorbed in the polymer-containing liquid phase at the end of the polymerization. Hence, the solution phase can be formed in a very small quantity, so that the polymerization reaction can be made to proceed in a good efficiency.
Incidentally, when substantially only the fluorine monomer is used, the polymer-containing liquid phase can be solidified into a waxy mass in many cases in the state it contains the organic solvent. In such cases, the fluorine-containing polymer can be readily taken out of the reaction vessel, and may be pulverized, followed by removal of the organic solvent to obtain a pulverized product of the fluorine-containing polymer with ease.
In the production process of the present invention, usable as the fluorine monomer is a fluorine-containing acrylic or methacrylic polymer having a polyfluoroalkyl group, represented by the following Formula (1) or (2):
Rfxe2x80x94Xxe2x80x94OCOCHxe2x95x90CH2xe2x80x83xe2x80x83(1)
xe2x80x83Rfxe2x80x94Xxe2x80x94OCOC(CH3)Hxe2x95x90CH2xe2x80x83xe2x80x83(2)
wherein Rf represents a polyfluoroalkyl group and X represents a spacer group.
Here, the polyfluoroalkyl group represented by Rf may preferably have 6 to 16 carbon atoms. This is because those having less than 6 carbon atoms make the resultant polymer tend to dissolve in the general-purpose solvent to make it difficult for the reaction mixture to be separated into the two phase, and those having more than 16 carbon atoms make the monomer itself available only at a greatly high cost to make it difficult to obtain polymers having properties good enough for the cost. Here, as examples of the polyfluoroalkyl group represented by Rf, it may include straight-chain or branched perfluoroalkyl groups represented by the following Formula (3) or (4):
CF3(CF2)nxe2x80x94xe2x80x83xe2x80x83(3)
(CF3)2CF(CF2)mxe2x80x94xe2x80x83xe2x80x83(4)
wherein n is a number of from 5 to 15, and m is a number of from 3 to 13.
It is also possible to use perfluoroalkyl groups a part of the fluorine atoms of which has bee substituted with a hydrogen atom(s).
In the monomer of Formula (1) or (2), there are no particular limitations on the spacer group represented by X, and any spacer groups used in commonly available monomers may be used, including, e.g., an ethylene group and ethyl (N-alkyl)sulfamides represented by Formula (5):
xe2x80x94SO2N(CpH2p+1)xe2x80x94CH2CH2xe2x80x94xe2x80x83xe2x80x83(5)
wherein p is 3 or 4.
In the present invention, the content of the fluorine monomer, i.e., the fluorine-containing acrylate or methacrylate in the total monomer may be appropriately selected in accordance with the intended properties of the polymer. However, its use in a too small content may not only make it impossible for the polymer-containing liquid phase to be separated, but also make the fluorine-containing polymer itself have poor properties in releasability or the like. Accordingly, it may preferably be in a content of at least 70% by weight, and more preferably at least 90% by weight.
As the non-halogen type solvent used in the present invention as the organic solvent, it is preferable to use an organic solvent having an intermediate solvent power, which is capable of dissolving the fluorine monomer, but is, with respect to the fluorine-containing polymer, neither a good solvent capable of dissolving the polymer in a free ratio nor a poor solvent almost not capable of dissolving the polymer or almost not capable of being dissolved into the polymer.
Such a non-halogen type solvent may include ketones or esters as those preferably usable. In particular, it is preferable to use at least one selected from the group consisting of ethyl acetate, propyl acetate, acetone, methyl ethyl ketone and methyl isobutyl ketone.
To specify any of these non-halogen type solvents, when the SP (solubility parameter) value (Polymer Handbook VII-519, Third Edition, 1989) indicating the degree of polarity is taken into account, a solvent preferably showing an SP value of from 8.0 to 10.5, and more preferably from 8.5 to 9.5, may be used as the non-halogen type solvent. Incidentally, fluorine type solvents commonly show SP values of 8 or below.
Among the non-halogen type solvents having SP values within such a range, those capable of being dissolved into the fluorine-containing polymer in an amount ranging from 10 to 50% by weight at polymerization temperature may preferably be used.
If the non-halogen type solvent is used in a too small quantity, the polymer-containing liquid phase may have so high a viscosity that the reaction mixture can be stirred with difficulty. If it is used in a too large quantity, no practical reaction rate may be attained and also residual monomers and oligomers may be formed in a large quantity. Accordingly, it may preferably be used in an amount of from 10 to 200 parts by weight, and more preferably from 20 to 150 parts by weight, based on 100 parts by weight of the fluorine monomer, the fluorine-containing acrylate or methacrylate.
In the production process of the present invention, a polymerization like the suspension polymerization may be carried out in an atmosphere of inert gas such as nitrogen gas, by the use of a known radical polymerization initiator (e.g., azobisisobutyronitrile, di-t-butyl peroxide and dibenzoyl peroxide) and at a temperature of preferably from 30 to 100xc2x0 C., and more preferably from 45 to 85xc2x0 C.
The polymer-containing liquid phase obtained as a result of the above polymerization solidifies upon cooling when the fluorine monomer is in a very large proportion of, e.g., 90% by weight or more, in the total monomer. Accordingly, the product thus solidified may be pulverized to readily obtain a powdery fluorine-containing acrylic or methacrylic polymer.